Figure 3.

Acoustic behavior of blue whales (Balaenoptera musculus)
in the Gulf of Corcovado, Chile, recorded on DTAGs
Alessandro Bocconcelli1,Mark Saddler2, Leigh Hickmott,3,4 Gustavo Chiang5,
Paulina Bahamonde, Francesco Caruso6, and Laela Sayigh2
(1)Woods Hole Oceanographic Institution, Applied Ocean Physics & Engineering, Woods Hole, USA
(2) Woods Hole Oceanographic Institution, Department of Biology, Woods Hole, USA
(3) Scottish Oceans Institute, East Sands, University of St Andrews, St Andrews, UK
(4) Open Ocean Consulting, Petersfield, Hampshire, UK
(5) Melimoyu Ecosystem Research Institute, MERI Foundation, Santiago, CHILE
(6) Institute for Coastal Marine Environment, National Research Council, Torretta Granitola, ITALY
INTRODUCTION
RESULTS AND CONCLUSIONS
Blue whales are known principally by two contrasting
accolades, first, as being the largest animal to have ever lived
on Earth, and second, as having been hunted to near
extinction during twentieth century whaling. During the
whaling era over four thousand animals were caught in
Chilean waters alone (Williams et al. 2011). The species has
been slow to recover from almost total decimation and hence
a valuable discovery was made in 1993, when a small blue
whale population of 232 individuals was found in the Gulf of
Corcovado in the Chiloense Ecoregion of Southern Chile
(Hucke-Gaete et al. 2004). Genetic, acoustic and
morphometric studies indicate that these blue whales are part
of a wider Southeast Pacific population that is distinct from
both the Antarctic (B. musculus intermedia) and “pygmy” (B.
musculus brevicauda) blue whale subspecies (Branch et al.
2007, Buchan et al. 2014, Torres-Florez et al. 2014). This
investigation set out to obtain data on the acoustic behavior of
individual blue whales in and around the Gulf of Corcovado,
Chile (Fig 1), through the deployment of suction cup attached
digital acoustic tags (DTAGs).
Seventeen tag deployments were achieved in 2014-2016,
for a total of 124 hours of data (Table 1). Acoustic data on the
tags have revealed a variety of different call types. These
include calls previously identified as “SEP2” calls (Southeast
Pacific; Buchan et al. 2014) (Fig 3), downsweep calls similar
to “D” calls described for blue whales in other areas (e.g.,
Oleson et al. 2007) (Fig 4), as well as several other call types.
Although we had hoped to attribute calls to the tagged
(focal) whales by confirming their occurrence on the tags’
accelerometers, we have found several lines of evidence that
suggest that the accelerometers are recording body vibrations
from received calls, as well as produced calls. First, we
sometimes see just a portion of a call on the accelerometers
(Fig 5). Second, we often see the six part SEP2 call
interrupted by surfacings (Fig 6). Finally, we see overlapping,
simultaneous calls on the accelerometers (Fig 7).
We are hoping to establish a threshold value for the
accelerometer signals above which we can confidently
conclude that that the call was produced by the tagged whale.
Tag data promise to enhance our interpretation of
recordings collected in this area from passive acoustic
monitors (PAM), both for species identification and possibly
also density estimation. Thus, this work has potential to
contribute to efforts to protect this important population of
endangered blue whales.
Our goal was to characterize the vocal repertoire of
individual whales using a technique described by Goldbogen
et al. (2014), in which the production of low frequency calls by
the tagged whale creates body vibrations that are recorded on
the tag’s accelerometers.
METHODS
DTAGs (v3) are sound and movement recording tags, which
are equipped with two hydrophones, a depth sensor, and 3-axis
accelerometers and magnetometers (Fig 2; Johnson and Tyack
2003). Accelerometers were sampled at frequencies ranging
from 200-500 Hz, which are high enough to detect most blue
whale calls (Goldbogen et al. 2014).
DTAGs are attached with four suction cups using a handheld 8m carbon fiber pole (Fig 2), and can be programmed to
release after durations of up to 24 hours. The tags contain a
VHF transmitter used to track the tagged whale during
deployment and to retrieve the tag after release.
An 18.6m fishing vessel, the MV Centinela, was employed
as the principle survey vessel. Field efforts were carried out in
February and March during 2014-2016, based on historical
sightings, acoustic detections, and weather data.
Figure 1. Map of the study region on the coast of Chile, showing
locations of sightings (“avistamientos”) and tag deployments, as
well as the cruise track (“recorrido expedicio”), for 2014 and 2015.
precursor notes
A2
B2
C2
D2
accelerometer signal
Figure 5 Spectrogram of an SEP2 call recorded on the
hydrophones (top panel), with only a portion of the call visible
on the accelerometers (lower 3 panels)
precursor notes
A2
B2 C2 D2
Acoustic data were downsampled in multiple steps from
either 120 or 500kHz and analyzed in MATLAB using DTAG
scripts (http://soundtags.st-andrews.ac.uk/dtags/dtag-3/) that
were modified for lower frequency baleen whale calls. Audio
spectrograms were viewed simultaneously with spectrograms
of the three accelerometer channels (e.g, Fig 4) in order to
document calls that were recorded on the accelerometers.
Figure 6. Spectrogram of an SEP2 call recorded interrupted
by a surfacing at approximately 3:10 (top panel: hydrophone;
lower 3 panels: accelerometers)
CONCLUSIONS
Figure 2. Upper left: DTAG being attached via a hand-held
pole; lower left: close-up of a DTAG; right: DTAG attached to a
blue whale
precursor notes
A2
B2 C2 D2
Figure 4. Spectrogram of two loud downsweep calls recorded
on the hydrophones (top panel) and also on all three
accelerometer channels (lower 3 panels)
Accelerometers appear to be recording body vibrations from
received as well as produced calls, which reduces their
usefulness for attributing calls to the tagged whale.
Nonetheless, tag data promise to enhance our interpretation
of recordings collected in this area from passive acoustic
monitors (PAM), both for species identification and possibly
7. Spectrogram
an SEP2
call
with overlapping
shortto
alsoFigure
density
estimation.ofThus,
this
work
has potential
tonal calls
appr 0855
(top panel:
3
contribute
toatefforts
to protect
thishydrophone;
importantlower
population
of
panels: accelerometers)
endangered blue whales.
BIBLIOGRAPHY
Branch, T. A., Abubaker, E. M. N., Mkango, S. and Butterworth, D. S. (2007). Separating southern blue whale subspecies based on length frequencies of sexually mature females. Marine Mammal Science, 23(4), 803–833.
doi:10.1111/j.1748-7692.2007.00137.x
Figure 3. Spectrograms of the previously described “SEP2”
call type produced by Chilean blue whales. This call consists
of six parts, labelled A2, B2, C2 and D2, plus two higher
frequency “precursor” notes, which are circled (Buchan et al.
2014). This loud call was recorded on a Marine Autonomous
Recording Unit (MARU) in the study area.
Buchan, S., Hucke-Gaete, R., Rendell, L. and Stafford, K. (2014). A new song recorded from blue whales in the Corcovado Gulf, Southern Chile, and an acoustic link to the Eastern Tropical Pacific. Endangered Species Research,
23(3), 241–252. doi:10.3354/esr00566
Goldbogen, J. A., Stimpert, A. K., DeRuiter, S. L., Calambokidis, J., Friedlaender, A. S., Schorr, G. S., Moretti, D. J., Tyack, P. L, and Southall, B. L. (2014). Using accelerometers to determine the calling behavior of tagged baleen
whales. The Journal of Experimental Biology: jeb-103259
Hucke-Gaete, R., Osman, L. P., Moreno, C. A., Findlay, K. P., and Ljungblad, D. K. (2004). Discovery of a blue whale feeding and nursing ground in southern Chile. Proceedings of the Royal Society of London. Series B: Biological
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Johnson, M. P., and Tyack, P. L. (2003). A digital acoustic recording tag for measuring the response of wild marine mammals to sound. IEEE Journal of Oceanic Engineering, 28(1), 3-12
Oleson, E. M., Calambokidis, J.,; Burgess, W. C., McDonald, M. A., LeDuc, C. A., and Hildebrand, J. A. (2007). Behavioral context of call production by eastern North Pacific blue whales. Marine Ecology-Progress Series, 30, 269 284
Torres-Florez, J. P., Hucke-Gaete, R., Rosenbaum, H. and Figueroa, C. C. (2014). High genetic diversity in a small population: the case of Chilean blue whales. Ecology and Evolution, 4(8), 1398–1412. doi:10.1002/ece3.998
Williams, R., Hedley, S. L., Branch, T. a, Bravington, M. V, Zerbini, A. N. and Findlay, K. P. (2011). Chilean blue whales as a case study to illustrate methods to estimate abundance and evaluate conservation status of rare species.
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